To determine whether poisoning with the organophosphate insecticide methamidophos results in a syndrome of persistent subclinical sensory and motor neuropathy, a clinical and epidemiologic study will be undertaken among a population of 50 seriously poisoned agricultural workers. Two comparison groups will also be examined -- one in which a history of methamidophos exposure is common, but with no history of poisoning, and the other with no history of exposure. Specific aims are: 1.To determine whether inhibition of lymphocyte neuropathy target esterase (NTE) measured in peripheral lymphocytes is a sensitive and specific index of peripheral neurotoxicity. 2.To determine whether previous poisoning with methamidophos results in diminished motor and sensory function, as reflected in electrophysiologic studies, pinch strength, and elevated vibrotactile threshold. 3.To determine whether a dose-response relationship exists between lymphocyte NTE inhibition and motor or sensory function. 4.To determine whether there exist threshold levels of methamidophos exposure below which either sensory or motor neuropathy is no longer evident. The public health significance of this study is that methamidophos and other organophosphate neurotoxins are widely used by workers in the United States and throughout the world.